On Aug 28, 2012, at 11:52 AM, Mauricio Cornejo wrote:
Peter,
You're right ... and I do think I've finally understood the help
file on this. I somehow missed the connection between my variable's
values, which include NAs, and the fact that those returned values
are in turn indices for '['.
OK ... I'm all straight on this now. (I lost count of how many
times I read the help file ... it'd be great if the help page could
be updated with a specific example on this sublety .... that's just
a thought).
I agree. An annotated example in the help page might help. I will post
such a suggestion to r-devel. (I include myself in those who sometimes
learn from example and counter-exampel better than we learn from
theory.)
--
David.
Thanks again to all for your patience with me on this,
Mauricio
New Jersey, USA
________________________________
From: Peter Ehlers <ehl...@ucalgary.ca>
Cc: William Dunlap <wdun...@tibco.com>; David Winsemius <dwinsem...@comcast.net
>; peter dalgaard <pda...@gmail.com>; "r-help@r-project.org" <r-help@r-project.org
>
Sent: Tuesday, August 28, 2012 2:08 PM
Subject: Re: [R] Inexplicably different results using subset vs
bracket notation on logical variable
On 2012-08-28 07:44, Mauricio Cornejo wrote:
William, David, and Peter,
Thank you all so much for your help on this. Though I had read the
help files on 'subset' and '[', I had not been able to discern from
that text what the problem was. I could not have solved it without
your help.
The help file on 'subset' mentions "For ordinary vectors, the
result is simply x[subset & !is.na(subset)]." However, since I was
dealing with a data frame at the time, I failed to appreciate the
relevance (but I get it now).
I've gone back to read the help on '[' and I still don't see where
this functionality is described. The page has section titled "NAs
in indexing", whose content I interpret as being limited to NAs in
the indices (and not in the returned values). I can't find any
text in the documentation describing the subtle behavior you kindly
pointed out.
Hmmm, it seems to me that the page is clear:
"... NA index picks an unknown element and so *returns* NA
in the corresponding element of ..."
(my emphasis)
Isn't that exactly what occurs?
Peter Ehlers
Thanks again,
Mauricio
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